ABSTRACT
Eighteen untreated, pilot treated and secondary treated bleach effluents from two pulp mills were studied in order to compare toxicity to a large number of elements and organic compounds. The toxicity tests used were: Pseudomonas putida growth inhibition, Vibrio fisheri luminescence bacteria test, Daphnia magna mobility inhibition, zebra fish (Brachydanio rerio) hatching and survival and Selenastrum capricornutum algae growth. General characteristics, BOD7, CODCr, TOC, loss on ignition, suspended solids, color, DCM extract, as well as specific compounds, AOX, totN, totP, 25 major and trace elements, phenolic compounds, fatty acids, resin acids, molecular weight (MW) distribution, terpenes and sterols, EDTA and DTPA were determined. A toxicity index (TI) based on EC50 and lowest effective concentration (LOEC) values of the three most sensitive tests was calculated for every effluent. CODCr, BOD7 and TOC showed the strongest positive correlation with TI (r = 0.928–0.774). Significant positive correlation with TI was observed for certain specific compounds as well: phenols, fatty acids, MW>10,000, AOX, totP, and MW<1,000, and Mn (r = 0.755–0.591). From the specific compounds, stepwise regression analysis selected phenols, fatty acids and resin acids as the best independent variables that explained 79% of the variance of TI. The correlation of AOX with toxicity was interpreted due to its correlation with other constituents in ECF and conventional effluents. The sum concentrations of phenols, fatty acids and resin acids in toxic dilutions of effluents exhibited levels comparable to EC50 values in the literature. Natural wood constituents were concluded to be responsible for most of the toxicity of the effluents studied.
